Many prey species have defensive tactics to escape being eaten by their would-be predators. But a study published in Current Biology on September 9, 2024 has taken it to another level by offering the first video evidence of juvenile Japanese eels escaping after being swallowed into the stomachs of their fish predators.

With the aid of X-ray videography, they found that the eels back their way out, first inserting the tips of their tails through the esophagus and gills before pulling their heads free.

“We have discovered a unique defensive tactic of juvenile Japanese eels using an X-ray video system: they escape from the predator’s stomach by moving back up the digestive tract towards the gills after being captured by the predatory fish,” said Yuuki Kawabata of Nagasaki University in Japan. “This study is the first to observe the behavioral patterns and escape processes of prey within the digestive tract of predators.”

In an earlier study, the researchers including Kawabata and Yuha Hasegawa had shown that Japanese eels can escape from the gill of their predator after capture. What they didn’t know was how.

“We had no understanding of their escape routes and behavioral patterns during the escape because it occurred inside the predator’s body,” Hasegawa says.

In the new study, they found a way to see inside the predatory fish (Odontobutis obscura) using an X-ray videography device. To visualize the eel after it had been eaten, they had to first inject them with a contrast agent. It still took the team a year to capture convincing video evidence showing the escape process involved.

Their videos show that all 32 captured eels had at least part of their bodies swallowed into the stomach of their fish predators. After being swallowed, all but four tried to escape by going back through the digestive tract toward the esophagus and gills, they report. Of those, 13 managed to get their tails out of the fish gill, and nine successfully escaped through the gills. On average, it took the escaping eels about 56 seconds to free themselves from the predator’s gills.

“The most surprising moment in this study was when we observed the first footage of eels escaping by going back up the digestive tract toward the gill of the predatory fish,” Kawabata says.

“At the beginning of the experiment, we speculated that eels would escape directly from the predator’s mouth to the gill. However, contrary to our expectations, witnessing the eels’ desperate escape from the predator’s stomach to the gills was truly astonishing for us.”

Further study found that, despite the similarities, the eels didn’t always rely on the same escape route through the gill cleft. Some of them also circled along the stomach, seemingly in search of a way out.

The findings are the first to show that the eel Anguilla japonica can use a specific behavior to escape from the stomach and gill of its predator after being eaten. It’s also the first time any study has captured the behaviors of any prey inside the digestive tract of its predator, according to the researchers.

The researchers say that the X-ray methods used in the study can now be applied to observations of other predator-prey behaviors. In future work, they hope to learn more about the characteristics that make for a successful escape by the eels.

A virtual haptic implementation technology that allows all users to experience the same tactile sensation has been developed. A research team led by Professor Park Jang-Ung from the Center for Nanomedicine within the Institute for Basic Science (IBS) and Professor Jung Hyun Ho from Severance Hospital’s Department of Neurosurgery has developed a technology that provides consistent tactile sensations on displays.

This research was conducted in collaboration with colleagues from Yonsei University Severance Hospital. It was published in Nature Communications on August 21, 2024.

Virtual haptic implementation technology, also known as tactile rendering technology, refers to the methods and systems that simulate the sense of touch in a virtual environment. This technology aims to create the sensation of physical contact with virtual objects, enabling users to feel textures, shapes, and forces as if they were interacting with real-world items, even though the objects are digital.

The technology is seeing increasing uses in the realms of virtual reality (VR) and augmented reality (AR), where it is used alongside visual and auditory cues to bridge the gap between the virtual and physical worlds.

Notably, electrotactile systems, which generate tactile sensations through electrical stimulation rather than physical vibrations, are emerging as promising next-generation tactile rendering technologies. The sensation of touch is mediated by mechanoreceptors, which are tactile sensory cells located in the skin that transmit tactile information to the brain in the form of electrical signals.

Electrotactile systems artificially generate these electrical signals, thereby simulating the sense of touch. Precise and varied tactile experiences can be created by adjusting current density and frequency.

Despite their potential, existing electrotactile technologies face challenges, particularly in safety and consistency. Variations in skin contact pressure can lead to unstable tactile sensations, and the use of high currents raises safety concerns. To address these issues, the IBS research team developed a transparent pressure-calibratable interference electrotactile actuator (TPIEA).

TPIEA comprises two main components: an electrode section responsible for generating electrotactile sensations and a pressure sensor section that adjusts for finger pressure. Researchers greatly reduced the impedance of the electrode by applying platinum nanoparticles to an indium tin oxide-based electrode.

This not only decreased impedance compared to conventional electrodes but also achieved a high transmittance of approximately 90%. The integrated pressure sensor ensures that users experience consistent tactile feedback regardless of how they touch the display.

In addition, the research team conducted a somatosensory evoked potential (SEP) test to quantify tactile sensations. By examining the responses of the user’s somatosensory system to variations in the current and frequency of electrotactile stimulation, they were able to quantitatively differentiate and standardize tactile sensations.

The team successfully implemented more than nine distinct types of electrotactile sensations, ranging from those resembling hair to those resembling glass, depending on the current density and frequency of the electrical stimulation. The team further demonstrated that the TPIEA could be integrated with smartphone displays to reliably produce complex tactile patterns.

Additionally, the research introduced interference phenomena into the realm of electrotactile technology. The interference phenomenon pertains to the alterations in frequency and amplitude that occur when two electromagnetic fields overlap.

This allowed the researchers to elicit the same intensity of electrotactile sensation with a current density that is 30% lower than previously required and to achieve an approximate 32% enhancement in tactile resolution. This research demonstrates the highest level of tactile resolution among current electrotactile technologies, including the Teslasuit.

Lead researcher Park Jang-Ung remarked, “Through this electrotactile technology, we can effectively integrate visual information from displays with tactile information. We anticipate that the findings of this research will significantly enhance the interaction between users and devices across various AR, VR, and smart device applications based on interference stimulation.”

Gray reef sharks are having to abandon the coral reefs they call home in the face of warming oceans, new research finds.

Scientists, using a combination of satellite remote sensing and a network of acoustic receivers on the seabed, have discovered that sharks are deserting coral reefs at times of environmental stress, such as high temperatures that can lead to coral bleaching events.

The effects on these sharks, normally strongly attached to particular areas of shallow reef habitats, include lower residency, more widespread and frequent movements to different areas and longer periods of absence entirely. Worryingly, these effects persisted for extended periods of up to 16 months following extreme stress periods such as the 2015-2016 El Niño event, which caused substantial bleaching in the study region.

The research is published in the journal Communications Biology.

As climate change is predicted to cause bleaching events annually by 2043, this behavioral change is “concerning,” say the scientists.

An international research team, led by marine scientists at Lancaster University and ZSL, attached acoustic trackers to more than 120 sharks and installed receivers around coral atolls to monitor shark movements at reefs in the Indian Ocean between 2013 to 2020.

They recorded more than 714,000 acoustic detections and, in collaboration with Earth Observation scientists at King’s College London, combined these with satellite data recording different metrics of reef environmental stress.

Scientists behind the study say this has important consequences for both the sharks and the reefs.

“These results provide some of the first evidence of how reef change in response to environmental stress, something that is becoming both more extreme and more frequent, is affecting the movement of sharks,” said Dr. David Jacoby of Lancaster University and principal investigator on the research project. “Gray reef sharks are a common, resident predator on the reefs of the Indo-Pacific, venturing away from the reef to feed, but many are having to decide whether to escape the stressed reefs.

“Faced with a tradeoff, sharks must decide whether to leave the relative safety of the reef and expend greater energy to remain cool or stay on a reef in suboptimal conditions but conserve energy. We think many are choosing to move into offshore, deeper and cooler waters, which is concerning. Many reefs around the globe have already seen significant declines in sharks due to exploitation and this finding has the potential to exacerbate these trends.”

Although the study didn’t examine the precise mechanisms linking reef stress to shark movement and residency, stress on coral reefs is often closely linked to sea surface temperatures.

“Sharks are ectotherms—cold-blooded animals whose body temperature is regulated by their external environment,” said Dr. Michael Williamson from ZSL’s Institute of Zoology, and lead author of the paper. “Reef sharks in other regions exhibit behavioral thermoregulation to avoid physiological damage from adverse water temperatures, and this is one of the potential drivers of the findings in this study.”

Importantly, sharks moving away could impact the fragile balance in reef ecosystems.

“As large predators, gray reef sharks play a very important role in coral reef ecosystems,” said Dr. Williamson. “They maintain a delicately balanced food web on the reef and they also cycle nutrients onto coral reefs from deeper waters where they often feed. A loss of sharks, and the nutrients they bring, could affect the resilience of reefs during periods of high environmental stress.”

Dr. Jacoby said, “As climate change brings increasing uncertainty and more and more frequent extreme stress events, the important ecological role these predators play on coral reefs is likely to change, as they spend more time away from the reefs they are attached to. The implications of this are not yet fully understood, but given the complex balance of species and trophic interactions that occur on coral reefs, there will certainly be substantial changes.”

However, there is also some room for optimism in the study’s findings.

Not all the monitored locations saw a decline in habitat use. In fact, some acoustic receivers at specific locations saw shark residency actually increase. These findings indicate that there could be localized factors influencing shark decisions, and that some reefs are more resilient to stress.

“We now need to find out what exactly is driving decision-making in these animals during periods of stressful conditions,” says Dr. Jacoby.

Although these factors were not included in the study, scientists suggest that different reefs can respond differently when exposed to stress.

“Recent research in the Chagos Archipelago, where we conducted our study, has shown that those reefs that have greater nutrient flows from seabirds have significantly enhanced fish biomass and therefore a higher likelihood to be resilient to multiple stressors,” said Dr. Williamson. “Some of our receivers that were seeing a greater number of sharks residing were also near islands with seabird populations.”

A new, cheap, easily manufactured device could lead to improved satellite communication, high speed data transmission, and remote sensing, scientists say.

A team of engineers led by researchers from the University of Glasgow have developed an ultrathin 2D surface that harnesses the unique properties of metamaterials to manipulate and convert radio waves across the frequencies most commonly used by satellites.

Metamaterials are structures that have been carefully engineered to imbue them with properties that don’t exist in naturally occurring materials.

The team’s metamaterial, unveiled today in a new paper published in the journal Communications Engineering, could allow future generations of 6G satellites to carry more data, improve their remote sensing ability, and benefit from improved signal quality.

Current communication antennas are designed to transmit and receive electromagnetic waves oriented either vertically or horizontally—a property called linear polarization.

Misalignment between transmitting and receiving antennas can lead to signal degradation, reducing their efficiency. They are also susceptible to atmospheric effects such as rain fading and ionospheric interference, which can distort signals.

The team’s breakthrough 2D metamaterial converts the linearly polarized electromagnetic waves into circular polarization, which could improve the quality of communication between satellites and ground stations. Satellite communication with circular polarization offers enhanced reliability and performance, minimizing signal degradation from polarization mismatch and multipath interference.

Circular polarization is highly resistant to atmospheric effects like rain fading and ionospheric disturbances, ensuring stable connections. It is especially beneficial in mobile applications, as it eliminates the need for precise antenna alignment.

It also doubles channel capacity by using both right-hand and left-hand circular polarizations. This flexibility simplifies antenna design for small satellites, while improving satellite tracking and providing robust communication links in challenging environments, making it ideal for modern satellite systems.

The team’s metamaterial, which is just 0.64mm thick, is made from tiny cells of geometrically patterned copper, which is laid over a commercial circuit board commonly used in high-frequency communications.

The surface of the metamaterial is designed to allow sophisticated reflection and repolarization of electromagnetic waves. In lab tests, the 2D metamaterial surface was illuminated by signals from horn antennas and the reflected electromagnetic wave was captured using a network analyzer, which allowed the team to measure the effectiveness of the device’s conversion between linear and circular polarization. The experimental results showed a close resemblance between simulated and experimental measurements for polarization conversion to circular polarization.

Their tests also showed that the surface is capable of maintaining high performance even when radio signals glance across it at angles of up to 45 degrees—a key consideration for space applications, where perfect alignment between satellites and the surface can be fleeting.

Professor Qammer H. Abbasi, of the University of Glasgow’s James Watt School of Engineering, is the paper’s senior and corresponding author. He said, “Previous developments in metamaterials have provided new ways for electromagnetic waves to be manipulated in devices with small form factors. However, they’ve largely been limited to narrow bands of the spectrum, which has limited their practical applications so far.

“The metamaterial surface we’ve developed works across a wide range of frequencies across the Ku-, K- and Ka-bands, which span 12 GHz to 40Ghz, and are commonly used in satellite applications and remote sensing.

“This kind of 2D metamaterial surface, capable of the complex task of linear to circular polarization, can enable antennae to communicate with each other more effectively in challenging conditions.

“It could help satellites provide better signals for phones, and more stable connections for data transmission. It could also improve satellites’ ability to scan the surface of the Earth, improving our understanding of the effects of climate change or our ability to track wildlife migration.”

Dr. Humayun Zubair Khan was a visiting postdoctoral student at University of Glasgow’s James Watt School of Engineering during the development of the metamaterial surface. Now at the National University of Sciences and Technology in Pakistan, he is the first author on the paper. He said, “This is an exciting development, which outperforms previously-developed technologies by a significant margin.

“Being able to manipulate and convert electromagnetic waves with a single piece of equipment opens up a range of new potential applications across the communications sector, but particularly in the space industry, where lightweight, compact materials are prized to help keep launch payloads down.”

Professor Muhammad Imran leads the University of Glasgow’s Communications, Sensing and Imaging hub, and is a co-author of the paper. He said, “One of the most exciting aspects of the metasurface we’ve developed is that it can be easily mass-produced using conventional printed circuit board manufacturing techniques.

“That means that it can be made easily and affordably, which could help it become widely-adopted in the years to come as a valuable piece of onboard equipment for satellites.”